The present invention relates to novel free-radically curable dental compositions, comprising chain-like and/or cyclic and/or cage-type polysiloxanes substituted by free-radically polymerizable groups and having at least 3 silicon atoms and/or mixed forms thereof, disiloxanes substituted by free-radically polymerizable groups, optionally one, two, three or more free-radically curable dental monomers having no silicon atom, fillers, initiators and/or catalysts for free-radical polymerization, and also further customary additives, to the cured dental products formed from the dental compositions of the invention, and to the respective use thereof as dental material, especially as flowable filling composites (called “flow materials”), core buildup materials and luting cements. The invention further relates to a process for producing the dental compositions and to a method for producing a respective dental product. Additionally claimed are inventive kits containing the novel free-radically curable dental compositions.
Further aspects of the present invention and preferred configurations thereof will become apparent from the description which follows, the working examples and the claims.
Polysiloxane compounds having at least 3 silicon atoms for the purposes of the present text have at least one chain or a plurality of chains having alternating and mutually connected silicon atoms and oxygen atoms, wherein the chains are also linked to form rings of different size, or to form even more extensive structures such as cages, and wherein organic groups (organic side chains) are bonded to the silicon atoms. These organic groups may be of chemically very different composition and hence lead to a multitude of polysiloxane compounds having different properties. Frequently, these organic groups have one or more organically polymerizable groups (i.e. reactive groups) which can react with, for example, one or more organically polymerizable groups in another polysiloxane compound and hence form crosslinked polymerized polysiloxane compounds. Chain, ring and cage structures may also occur in the form of mixed structures. They are likewise part of the dental compositions of the invention.
Polysiloxane compounds have long been known and are obtainable, for example, by hydrolysis and condensation of silanes having hydrolyzable groups (see, for example, DE 27 58 414 A1) or by hydrosilylation of allyl or vinyl compounds with SiH-containing compounds. Polysiloxane compounds can be processed further to give a multitude of products, for example overlayers, coatings, membranes or bulk materials. This further processing is frequently based on a crosslinking reaction of organically polymerizable groups in the polysiloxane compounds (e.g. (meth)acrylate groups) and the resulting formation of crosslinked polysiloxane compounds.
“(Meth)acryl . . . ” is understood in the context of the present text to mean both “acryl . . . ” and “methacryl . . . ”.
A specific group of polysiloxane compounds contains, in the organic groups (side chains), besides an organically polymerizable group, additional free polar functional groups, for example hydroxyl or carboxyl groups.
For instance, DE 44 16 857 C1 relates to hydrolyzable and polymerizable silanes, to processes for preparation thereof and to the use thereof for production of silica (hetero)polycondensates and (hetero)polymers. Hydrolyzable, organically modified silanes find wide use in the production of scratch-resistant coatings for a wide variety of different substrates, for the production of fillers, of adhesives and sealing compounds or of shaped bodies.
DE 44 16 857 C1 discloses the use of silica (hetero)-polycondensates (polysiloxane compounds) in curable dental materials. The polysiloxane compounds described here comprise free polar functional groups (e.g. carboxyl or hydroxyl groups) capable of complexing suitable metal ions/transition metal ions (e.g. ions of titanium, zirconium or tin). In curable dental compositions, this can have a positive effect on x-ray opacity, on contact toxicity and on the refractive index of a corresponding curable or cured dental material.
DE 198 60 364 C2 relates to polymerizable dental compositions based on siloxane compounds that are capable of curing, and to the use and production thereof. This publication describes the preparation of cyclic polysiloxanes and the use thereof as a basis for polymerizable dental compositions. In spite of high density of groups capable of polymerization, they are said to have a low viscosity which enables high filler loading, which leads to compositions having low polymerization shrinkage. Here too, free polar functions are present as well as the polymerizable units in the organic side chains of the polysiloxanes described.
The free polar functional groups, for example in the aforementioned polysiloxane compounds, however, regularly lead to unwanted properties too. For instance, it has been found that the hydrophilicity of the polysiloxane compounds caused by the (free) polar functional groups leads to increased water absorption in the presence of moisture, which reduces the wet strength of the curable dental material in a disadvantageous manner. Probably due to the formation of internal hydrogen bonds, there is an increase in viscosity. This then has an adverse effect on handling in the production of the curable dental compositions.
There is a considerable need on the part of dental practitioners and the dental industry to adapt polysiloxane compounds further to the demands on a modern (curable or cured) dental material and to minimize the aforementioned disadvantages. Polysiloxane compounds adapted in such a way should have improved physical properties for dental purposes (i.e. lead to dentally improved physical properties of the corresponding curable/cured dental materials), for example lower polymerization shrinkage on polymerization/crosslinking of the polysiloxane compounds (i.e. on curing), increased strength and/or restricted water absorption with simultaneously comfortable consistency of the curable dental material.
The first successes in the improvement of the polysiloxanes were achieved through addition or substitution of different substrates onto the free polar functionalities of the above-described specific polysiloxanes.
EP 1 874 847 B1 relates to a process for preparing silanes having two, three or even more structural units linked together by a urethane-, acid amide- and/or carboxylic ester-containing bridge, each of which contains at least one organically polymerizable radical and at least one silyl radical. These silanes should especially be suitable for modification of the properties of silicic acid (hetero)polycondensates and silyl-containing organic polymers. The process disclosed should also be suitable for bridging of already precondensed silicic acid (hetero)polycondensates.
The silicic acid (hetero)polycondensates (polysiloxane compounds) disclosed in EP 1 874 847 B1 have a free hydroxyl group (i.e. a free polar functional group). These free hydroxyl groups can react with a dicarboxylic acid derivative or diisocyanate such that hydroxyl groups form a link (bridge) with a dicarboxylic acid derivative or diisocyanate. Such linked polysiloxane compounds have a much higher molecular weight without any significant reduction in the double bond density (as a result of the organically polymerizable (meth)acrylate groups). Double bond density is understood here to mean the quotient of the number of polymerizable double bonds in a compound and the molecular weight of this compound. The higher molecular weight has a positive effect on biocompatibility and polymerization shrinkage on crosslinking of the linked polysiloxane compounds. At the same time, the hydrophobicity of the polysiloxane compounds was increased. However, it has been found that the higher molecular weight has an adverse effect on the viscosity of the linked polysiloxane compounds (and hence on processibility in manufacturing the curable dental material). The viscosity rises markedly with the degree of crosslinking, i.e. with the molecular weight, such that there is no longer satisfactorily tolerable processibility in manufacturing a corresponding curable dental material comprising such linked polysiloxane compounds, even at quite a low degree of linkage.
EP 1 685 182 B1 relates to silanes and silicic acid polycondensates and partial condensates formed therefrom, in which an organic radical bonded to a silicon is present, which is branched and bears an independently organically polymerizable group at each of the two branches, or bears such a group at one of the two branches and has a radical having a further silicon atom at the other.
The polysiloxane compounds disclosed in EP 1 685 182 B1 also comprise free polar functional groups in the form of hydroxyl groups. By reaction of carboxylic acid or isocyanate derivatives which themselves likewise comprise polymerizable double bonds (e.g. (meth)acrylate groups), it is thus possible to link organically polymerizable groups onto free polar functional groups. These reaction products regularly have elevated strength with simultaneously increased hydrophobicity and improved biocompatibility due to the elevated molecular weight.
However, in these cases too, it has been shown that the introduction of additional polymerizable double bonds leads to increased polymerization shrinkage on crosslinking of the polysiloxane compounds, since the double bond density is markedly increased, but the increase in the molecular weight is only comparatively small.
WO 2013/041723 A1 discloses hydrolyzable and polymerizable silanes (including silicic acid polycondensates, i.e. siloxanes) having adjustable spatial distribution of the functional groups, and the use thereof. The teaching disclosed in WO 2013/041723 A1 relates to a method for chain extension of radicals bonded to silicon via carbon in silanes or siloxanes.
WO 2013/053693 A1 discloses silicic acid polycondensates (siloxanes) having cyclic olefin-containing structures and methods for preparation thereof, and the use thereof. WO 2013/053693 A1 discloses that polymer materials having moduli of elasticity adjustable within wide limits combined with high elastic strain (i.e. without brittleness) and hence high fracture toughness can be produced from silicic acid (hetero)polycondensates having cyclic olefin-containing structures.
The as yet unpublished DE 10 2014 210 432 describes polysiloxane compounds which have the aforementioned disadvantages from the prior art in a curable or cured dental composition at least only in attenuated form, if at all. The conceptual approach to these systems is based on the idea of converting the free functional group in the silane such that no additionally polymerizable double bonds are introduced into the system. Instead, hydrocarbyl radicals of high molecular weight having at least 11 carbon atoms are incorporated into the system. Surprising findings in the case of these curable dental compositions were                a good viscosity of the polysiloxane compounds (the viscosity should be 50 Pa*s or less at a temperature of 25° C.) and an associated excellent processibility in the production of a curable dental material containing the polysiloxane compounds,        good hydrophobicity,        good strength, especially good flexural strength,        very low polymerization shrinkage on crosslinking of the polysiloxane compounds, i.e. on curing of the curable dental material,        good biocompatibility,        a refractive index almost identical to the refractive index of standard dental glasses.        
The measures taken in DE 10 2014 210 432 thus solved several problems at once:                Elimination of polar functional groups prevented the formation of intermolecular interactions. It was thus possible to keep the viscosity of the system at a comparatively low level in spite of a remarkable increase in molecular weight.        Incorporation of hydrocarbyl radicals of relatively high molecular weight resulted in widening of intramolecular spacing in the polysiloxane structure, and so it was possible to increase the accessibility of the free-radically polymerizable groups during the curing and hence to optimize the conversion rate. How else could one explain the fact that in these systems, with a comparatively reduced double bond density, the strength of the materials, for example the flexural strength of the cured dental compositions, remains at a very good level and in many cases is actually increased compared to the polysiloxanes without further conversion.        The increase in molecular weight with the same functionality, i.e. in the case of an effective lowering of the double bond density, made it possible to adjust especially what is perhaps the clinically most important technical parameter for a curable dental composition, namely the value of the volume shrinkage during the curing, to an extremely low value. In clinical practice, therapeutic success is also dependent primarily on whether the dental material, for example, seals a cavity prepared by the dentist with high marginal integrity. As a result of shrinkage of the material in the course of polymerization, marginal gaps can form, through which bacteria penetrate into the tooth and then cause the treatment to fail.        Incorporation of hydrocarbyl residues of relatively high molecular weight also made the polysiloxane structure comparatively hydrophobic, such that the unwanted absorption of water now adopts extremely low values.        
The free-radically curable compositions described in DE 10 2014 210 432 are especially suitable for use in a therapeutic method for temporary or permanent filling of a dental cavity. The systems are additionally suitable for use in a therapeutic method as base material, as adhesive (bonding), as a flowable composite material (flow material), as a fissure sealant, as a crown and bridge material, as an inlay/onlay and/or as core buildup material.